Preheat oven to 350 degrees F.
Cook the jumbo pasta shells according to package directions, about 9 minutes. Drain and run under cold water so they don’t stick together, being careful not to break them. Set aside.
Make the filling: In a bowl, combine the ricotta, 1 ½ cups of the mozzarella cheese, ½ cup of the parmesan cheese, eggs, garlic powder, Italian seasoning, fresh basil, fresh parsley, spinach (thawed and excess moisture squeezed out), salt, and pepper. Mix until well-combined.
Spread a layer of marinara sauce on a 9x13 inch baking pan.
Using a cookie scoop, fill the shells with the prepared filling (a cookie scoop cleanly, easily, and evenly releases the filling). Alternatively, you can add the filling to a resealable plastic bag with the corner snipped off and pipe into the shells. Or simply use a spoon.
Arrange the filled pasta shells on top of the layer of marinara sauce, open side up.
Spread some more marinara over the shells, to taste. Top with remaining 1 ½ cups of mozzarella and ½ cup of parmesan cheese. Note: Feel free to adjust the amount of cheese to your liking.
Cover with aluminum foil and bake for 25 minutes. Remove foil and bake for another 5-8 more minutes until the cheese is melted. Then, broil on high for 2-3 minutes until slightly golden brown and bubbling. Let cool down slightly and serve. Enjoy!